Stretch wrapping fixture and combination thereof with drawing dies and press



Feb. 1 I, 1969 Q J A ET AL STRETCH WRAPPING FIXTURE AND COMBINATIONTHEREOF WITH DRAWING DIES AND PRESS of 4 I Sheet Filed Jan. 11. 1967 Wam?- W r/4 7705x05 c. J. BATH ET L STRETCH WRAPPI Feb. 1 1

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STRETCH WRAPP ING FIXTURE AND COMBINATION THEREOF WITH DRAWING DIES ANDPRESS Filed Jan. 11, 1967 Sheet 4 of 4 United States Patent 3,426,570STRETCH WRAPPING FIXTURE AND COMBINA- THEREOF WITH DRAWING DIES ANDCyril J. Bath, Chagrin Falls, and John H. Leonard, Hudson, Ohio,assignors to The Cyril Bath Company, Cleveland, Ohio, a corporation ofOhio Filed Jan. 11, 1967, Ser. No. 608,669 U.S. Cl. 72-296 Claims Int.Cl. B21d 11/02, 11/22; B21 9/18 ABSTRACT OF THE DISCLOSURE The stretchdraw fixture is employed in a drawing die press, one fixture at each endof the set of drawing dies. Each fixture includes a gripping head whichgrips the adjacent end margin of the sheet. The heads are arranged fortensioning a sheet of metal unidimensionally into the yield range whilewrapping it onto the forming face of the male die, preparatory toclosure of the dies. Each head is supported by linkages which arepivotally connected at one end to the male die and at the other end tothe head. The pivotal axes of each linkage define a quadrilateral withaxes extending transversely of the direction of tensioning of the sheet.The linkages cause the heads to move apart for tensioning the sheet asthe heads are moved by power means in the direction for laying the sheetonto the male die.

This invention relates to a stretch draw fixture and combination thereofwith a drawing die press, and is an improvement on the inventionsdisclosed in United States Letters Patent of Cyril J. Bath, No.3,116,780, issued Jan. 7, 1964, in the application of Robert A.Mackenzie, Ser. No. 514,219, filed Dec. 16, 1965, entitled, PrestretchFixture and Combination Thereof With Drawing Die Press, whichapplication was abandoned in view of the filing of an application ofRobert A. Mackenzie, Ser. No. 475,487, filed Aug. 12, 1966, now US.Patent No. 3,314,269, issued Apr. 18, 1967, and in the application ofCyril J. Bath, Ser. No. 550,520, filed May 16, 1966, and entitled, LinkSupported Gripping Head.

In the above-entitled patent there is disclosed a conventional drawpress employing complementary drawing dies combined with stock grippingstretch heads which are operable by hydraulic piston and cylinderassemblages to tension a sheet of metal stock unidimensionallypreparatory to and during drawing of the stock by and betweenconventional drawing dies. The stretch heads are mounted on carrierswhich are movably connected to elevators and support the heads forhorizontal movement, relative to supporting elevators, toward and awayfrom each other for tensioning the stock. The elevators, in turn, aremounted on a frame for vertical sliding movement and are power driven,by hydraulic piston and cylinder assemblages or other means, forlowering and raising the carriers, and thereby the heads, so as to wrapthe tensioned stock about the male die preparatory to die drawing thestock to final shape. The heads are maintained in substantialparallelism with their starting position at all times. Such a structure,with tension controls, are very desirable for stretch drawing the moreexotic metals and alloys wherein considerable flexibility in timing andintensity of applied forces is required from piece to piece of stock dueto the nonuniformity of the stock and the closeness of yield to ultimatestrength. This structure, while highly effective in such applications,is expensive, due particularly to the hydraulic piston and cylinderassemblages used for moving the heads and the elevators, and the cyclingcontrols required.

3,426,570 Patented Feb. 11, 1969 One manner of simplifying the stretchhead mountings by connecting the stretch heads to the elevators withgenerally upright parallelogram linkages is disclosed in the above Bathapplication. In that case, the elevators were retained, but the slidesand guideways thereon for the head carriages were eliminated. Theparallelogram linkages connected each head directly to its elevator sothat the head was constrained to swing relative to its elevatorsubstantially horizontally in a direction toward and away from the dieand to remain substantially parallel with its starting position.

However, in high speed production of sheet metal automobile body parts,like precision in tensioning forces applied and variation in timing andcontrol is not necessary because of the much greater spread between theyield point and ultimate strength of the sheet steel customarily usedfor automobile. body stock. Instead, variability in cycling andapplication of precise tensioning forces becomes secondary to speed inproduction and dimensional precision in the length of the uutrimmedformed sheet of stock so that the uutrimmed formed sheet can beaccommodated readily and properly in subsequent trimming dies and thelike.

In automotive body production, substantially-all parts are asymmetricalwith respect to an upright median plane extending transversely of thepart at the longitudinal midportion of the sheet stock. It was found,however, as disclosed in the above Mackenzie application, that withlinkages of proper lengths for the respective stretch heads and dies,and with the pivot points located in proper position relative to thedies and to the heads or their carriages, the heads could be caused tofollow precise preselected paths repeatedly such that the heads wouldcooperate properly and consistently with asymmetrical drawing dies andduplicate both the parts and the shape and overall dimensions of theformed, but uutrimmed, sheet of stock.

The elevators for the head carriers were retained and the linkagesconnected the carriers to the elevators, the elevators insuring that theheads would remain substantially parallel to their starting or loadingpositions while moving toward and away from each other during tensioningof the stock and upwardly and downwardly during wrapping the stock aboutthe male die. This assured that the heads could approach very closelythe ends of the dies, thus reducing the length of the sheet required fora given part or group of parts.

However, a problem still remained as to actuating the stretch headsextremely rapidly with hydraulic piston and cylinder assemblages whensubject to the heavy inertial forces inherent in reciprocating themassive elevators and the parts carried thereby. Also, the elevatorsoccupied a very substantial portion of the available die space of thepress, and were large and expensive fabrications.

The present invention provides a structure essentially the same as thatin the Mackenzie application except that the elevators are eliminatedand, instead, the stretch heads are both supported and guided alongprecise paths and maintained in parallelism with their loading positionsduring the stretch drawing operation by means of head supportingparallelogram linkages of which the pivotal axes at one end of thelinkages are in fixed relation to the male die and at the other are infixed relation to the associated stretch head. As a preferred example,instead of a pair of single links, arranged one at the front and one atthe rear of each head, and having common :pivotal axes, as in theMackenzie application, one or more pairs of links are provided, eachpair comprising at least two parallel links of equal length pivotallyconnected each at one end of the pair with their pivotal axes in fixedrelation to the die and at its other end of the pair to the head withtheir pivotal axes in fixed position relative to the heads.

The intersections of the pivotal axes of the pair of links of a givenparallelogram linkage with a plane normal to these axes, define aparallelogram, and each such an arrangement of two links is aparallelogram linkage whether the two parallel links are coplanar or aredisposed in parallel planes in spaced relation to each other endwise ofthe pivotal axes. Such a parallelogram linkage supports the associatedhead and maintains it parallel to its original starting or loadingposition during operation and constrains the head to follow precisely toits proper predetermined path invariably. Such linkages hold the headsin the proper horizontal position for ready loading of the stock andremoval of the formed sheet.

In the present invention, not only have the tensioning piston andcylinder assemblages interconnecting the stretch heads and theirelevators been eliminated, but also, the elevators themselves have beeneliminated, thus greatly simplifying the structure and reducing theweight and resultant inertial forces. Since tension sensing andresultant control generally are not required for such production, thecarrier may be made rigid with, or an integral part of, the stretchhead. If sensed tension and control thereby should be desired in aspecific instance, the carrier need be merely a plate with the headinterconnected with the plate by tension sensing bars and mounted on theplate for extremely limited relative movement toward and away from thedies.

Specific objects and advantages of the invention will become apparentfrom the following description wherein reference is made to thedrawings, in which:

FIG. 1 is a front elevation of a conventional power driven drawing diepress with the improved stretch wrapping fixture of the presentinvention combined therewith;

FIG. 2 is an enlarged fragmentary right side elevation, partly insection, of the fixture and a part of the press shown in FIG. 1, asviewed from the line 22 in FIG. 1, and showing the parallelogram linkageemployed;

FIG. 3 is an enlarged fragmentary top plan view of a portion of the:press and the fixture illustrated in FIG. 2, viewed as indicated by theline 3-3 in FIG. 1.

FIG. 4 is a hydraulic diagram showing the supply of hydraulic fluid foroperating the apparatus, the timing controls being omitted because notpart of this invention;

FIG. 5 is a fragmentary diagrammatic front elevation of the stretchwrapping fixture of the present invention illustrating a differentpositioning of links for providing parallelogram linkage for the stretchheads;

FIG. 6 is a fragmentary diagrammatic top plan view of the structure ofFIG. 5;

FIG. 7 is a fragmentary diagrammatic front elevation of the stretchwrapping fixture illustrating another positioning of links for providinga parallelogram linkage;

FIG. 8 is a fragmentary diagrammatic top plan view of the structureillustrated in FIG. 7;

FIG. 9 is a diagrammatic perspective view of another form ofparallelogram linkage used in the present invention; and

FIG. 10 is a diagrammatic top plan view of the structure illustrated inFIG. 9.

Referring to the drawings, a preferred form of the invention isillustrated wherein a stretch wrap fixture of the present invention isshown installed in a conventional upright hydraulic press 1 having a bed2 with upright guide members 3 arranged at the corners and guiding apower driven ram 4 for vertical reciprocation. A male die 5 having aforming face which is convex upwardly both lengthwise and transverselyis supported on the bed 2, and a companion female die 6 is mounted onthe ram 4. Conventional holddown rings or devices are not employed asthe stock is left free to draw in transversely of the tensioningdimension.

The invention, being particularly desirable for combined stretching anddie drawing of sheet metal automotive body stock and the like intoshapes which are nonsymmetrical about an upright median line extendingtransversely of the tensioning dimension, the male die is shown asasymmetrical endwise.

The ram is driven on its forming and return strokes by means ofhydraulic piston and cylinder assemblages 7, including cylinders 8 andpistons 9, having rods 10 connected to the ram. The stretch wrappingfixture generally includes two units 11 arranged on the bed 2 at the twolimits of the male die which are opposite each other in the tensioningdimension. Regardless of whether the tensioning dimension is the longeror shorter dimension of the work piece or die, it is considered theendwise dimension.

Each unit 11 comprises a stretch head 12 having a pair of jaws 13operated for opening and closing through linkages 14 by piston andcylinder assemblages 15, thereby to grip the associated margin of thesheet of stock for applying tension thereto upon movement of the headalong its predetermined path. Each head is mounted on a carrier 16which, if desired, may be in the form of a plate rigid with the maincasting or body of the head 12, or may be an integral part thereof. Thehead 12 is elongated forwardly and rearwardly of the press. At itsforward and rearward ends, it is provided with fixed gussets or brackets.17, respectively, rigid with the head 12 and carrier 16.

For raising and lowering the heads, a plurality of hydraulic piston andcylinder assemblages 18 are provided for each head. Each assemblagecomprises a cyl inder 19 carrying a piston 20 having a rod 21 pivotallyconnected by a pivot 22 to a suitable bracket on and rigid with, thecarrier 16. The lower end of the cylinder 19 is pivotally connected by apivot 23 to a suitable bracket 24 which is connected in fixed positionrelative to the bed 2 of the press.

With the structure thus far described, it is apparent that the stretchheads 12 can be moved toward and away from each other generallyhorizontally for tensioning a sheet of stock S and concurrently can bemoved vertically by the assemblages 18. However, to apply the properstretching forces and assure that all sheets of a lift of like sheetswill be substantially identical in shape and dimension when formed andbefore trimming, the heads are constrained to move parallel to theirloading positions, each in a fixed invariable path so as to provideconcurrently the desired components of horizontal and vertical movement.In order to constrain each head 12 to move in its selected path, chosenso that the stock is always properly tensioned during the wrapping ofthe stock on the die, parallelogram linkages are provided.

Referring specifically to the right hand unit 11 illustrated in FIG. 1,the parallelogram linkage shown for illustration comprises rigid rods orlinks capable of withstanding the endwise compression without bucklingor distortion and arranged in pairs, preferably one pair at the frontend of the head 12 and one pair at the rear end of the head 12. All ofthe links are of equal length and all are parallel to each other. Thelinks of each pair are spaced from each other transversely of theirpivotal axes. Each link 25 is pivotally connected at one of its ends bypivot 26 to an associated one of the brackets 17. The axes of the pivot26 at this end of the pair extend parallel to each other and are infixed relation to the gusset 17 and head 12. The opposite ends of thelinks 25 are pivotally connected by pivots 27 to a rigid supportingmeans which, in the form illustrated, is shown as an integral bodyportion of the die 5, but which may be a detachable separate bracket orthe like mounted in fixed position relative to the die 5.

The pivots 27 are parallel to the pivots 26 and are arranged the samedistance apart so that the intersection of the axes of the four pivotsof each parallelogram linkage with a plane normal to the axes define aparallelogram. The parallelograms defined by each parallelogram linkagefor a given head are identical with each other and preferably arearranged so that corresponding pivots 26 and 27 of one pair are coaxialwith other pair of the same head, if any, essential.

The links form one pair of opposite sides of the parallel linkage. Theother pair of opposite sides of the same linkage may be separate links,but it is convenient instead to allow the rigid portion of the die body'5 and of the gusset 17 to function as such. All the pivots 25 and 26,and all of the links 25 of all of the parallelogram linkages, if morethan one linkage is used, are parallel to each other and the links areall the same length. However, the parallelogram linkages, if more thanone per head is employed, need not have their corresponding pivotal axesat the same elevation or in the same position endwise of the die, solong, however, as the parallelograms themselves are identical and havetheir corresponding axes parallel.

'In the case of some specialized dies, a stationary gripping head may beused at one end of the male die opposite from a single head 12, but mostgenerally two companion units are desirable and necessary.

Referring to the left hand unit in FIG. 1, it is the same in allrespects as the right hand unit, except that the links 30 of eachparallelogram link-age are generally of different lengths than the links25 and the pivots 31 may be differently arranged relative to each otherand to the die. Of course, in those few instances in which the die faceis symmetrical about its median line, the parallelogram linkages of thetwo units may be identical in shape, size, and position relative to themale die. In the right hand unit, at least two parallelogram linkagesare provided which are arranged so that at all times they are parallelto each other. The specific length of links 30 and positioning of thepivots 3.1 and 32 are readily selected in relation to the shape of thedie between its crest and the end adjacent the particular unit.

The units 11 are arranged so that preferably, while the metal is eitheruntensioned or lightly tensioned, the heads move down until the sheet Sengages the crest of the male die. They continue moving and by the timethe metal is in firm engagement with the crest, or shortly thereafter,they have moved apart from each other so as to tension the stock into arange above the elastic limit so that it reaches the yield point.

It is to be noted, for example, that this is eflected'in the case of thelinks 2'5, as illustrated in FIG. 1, because as the right hand head 12moves downwardly, it moves away from the die 5, thus tensioning thestock, until the links 25 become horizontal or at dead center relativeto their pivots. The head then no longer moves away from the die, butsince a substantial amount of metal is being wrapped onto the formingface of the die, even though the head moves toward the die, it does notmove toward the die as rapidly as the stock is foreshortened end'wise ofthe die 5, by being stretch wrapped about the die face.

Referring to FIG. 4, the unit and press may be operated from a pump 35driven by a motor 36, pressure fluid being fed to the assemblages 7 ofthe press through'a suitable reversing and stop valve 38 so as to raiseand lower the ram, selectively. Also, pressure fluid is supplied fromthe pump 35 through reversing valves 39 to the piston and cylinderassemblages 15, respectively, for opening and closing the jawsindependently of each other. Fluid from the pump also is deliveredthrough reversing and stop valves 40 to the piston and cylinderassemblages 18, respectively, for raising and lowering the headsindependently of each other.

Thus, each piston and cylinder assemblage 18, by pulling downwardly onthe associated head while the head is constrained by the parallelogramlinkage to swing in an invariable fixed path and parallel to itsstarting or load ing position causes the linkages to apply the requisitetension to the stock. If desired, of course, instead of the assemblages18, suitable pressure applying push rods those of every though this isnot may be provided on the ram for driving the heads downwardly, asdescribed, for example, in the application of Stanley M. Donley, Ser.No. 517,616, filed Dec. 30, 1965, and entitled, Hydraulic Push Rod forStretch Draw Press. If push rods are used, lighter piston and cylinderassemblages, located as are the piston and cylinder assemblages 18, maybe used to apply light yieldable resisting pressure to raise the headswhen the ram and push rods are not forcing them downwardly.

It is apparent that this arrangement, with the heads 12 in the fullyraised position illustrated in FIG. 1, the margins at the ends of thesheet of stock S are gripped in the jaws 13, whereupon the ram isstarted on its downward stroke to lower the die 6. The assemblages 18begin lowering the heads 12. As the heads lower, they may apply lighttension or substantially no tension on the stock. The choice of lengthof the parallelogram linkages and location of the pivots is such thatthe stock engages the crest of the male die 5 before the stock istensioned to a degree which would cause fluting or wrinkling. However,after the stock engages the crest, the heads continue downwardly andtension the stock into the yield range, above the elastic limit and thenwrap the stock while thus maintained under tension, onto the male die.After the parallelogram linkages pass dead center, the heads beginmoving back toward the die 5, but at a rate such that, due to the amountof the sheet stock wrapped on the die, the tension is still maintainedduring the inward movement. This operation continues until the stock isfully wrapped on the die 5. With the properly selected length of thesheet S, the inboard faces of the gripping jaws, adjacent to the die,move substantially to the end limits of the die. When the heads reachthis relative position and the stock is thus fully wrapped, it is struckby the female die 6 which completes formation of the article, as in theconventional draw die operation.

Thus, it will be seen that the relatively large and expensive elevators,slide mountings of the heads or carriages thereon, the banks of stretchforming assemblages, and raising and lowering assemblages of the largesize heretofore required are eliminated. The parts required are so fewand inexpensive that each die and its stretch heads and linkages can beretained and stored as a unit without disturbing the relation betweenthe heads and the forming surfaces of the dies. This assures: that atany time replacement parts are to be made they will be duplicates of theoriginal car production. In this connection it might be noted that thepiston and cylinder assemblages 18 may be proportioned for theparticular head with which it is associated so that they have exactlythe right starting and stopping points both in lifting and lowering. Ifso, they carrremajn attached to, and stored with the units. On the otherhand, if the strokes of these assemblages are to be variable andotherwise controlled, then of course these assemblages can be detachedfrom the associated units by detaching the pivots, such as 22 and fordifferent dies and stretching and wrapping assemblages.

In the form illustrated, twoparallelogram linkages are provided for eachhead. More may be provided, or, if desired, single parallel linkage ofsufficient strength may be used.

If several parallelogram linkages are used for a given head, theparallelograms defined by them have their corresponding pivots coaxial.However, this is not essential. As illustrated in FIGS. 5 and 6, forexample, there are shown two identical parallelogram linkages 42 and 43.It is to be noted that while the parallelograms defined by theselinkages are parallel and of the same size and shape in any givenposition of the associated stretch head, the axes of the four pivotalaxes at corners of one linkage are not coaxial with the correspondingaxes of the other, transversely of the axes therefrom.

In FIGS. 7 and 8 are shown two identical parallelogram linkages 44arranged with the two ends of each parallelogram linkage disposed inparallel planes which are offset endwise of the pivotal axes.

Thus, identical parallelogram linkages may be arranged with the twolinks of each linkage in a common plane or in respective planes parallelto each other and spaced apart endwise of the axes, and withcorresponding axes coaxial are offset radially from each other. Again,pairs of parallelogram linkages may be offset transversely of the axes.However, in all cases, the parallelograms defined by the axes must beidentical and with their corresponding sides parallel.

FIGS, 9 and 10 illustrated a modification of the linkage in which only asingle parallelogram linkage is provided for an associated stretch head.In this form a stretch head 45 is provided at its sides with supportingplates or brackets 46 between which a single rigid parallelogram linkageis disposed. The parallelogram linkage comprises an upper link 47 and alower link 48, these links being in the form of castings orfabrications, each including a generally horizontal portion 47a and avertical portion 47 b extending upwardly therefrom. By having thehorizontal and upwardly extending portions, the links can be connectedto the die by pivots 49 so as not to interfere with the die and to thehead 45 by pivots 50. The links of a pair in a given parallelogramlinkage may be substantially identical, and similar to the single linksdisclosed in the above copending application of Robert A. Mackenzie,Ser. No. 514,219, filed Dec. 16, 1965.

It is to be noted that in the above-entitled application, Ser. No.550,520, parallelogram linkage means constrain the head to movementwhich is approximately horizontal relative to an elevator which is thesupporting means to which are connected the ends of the links oppositeto the ends connected to the head. This elevator provides essentiallyall vertical components of movement for wrapping the stock about a diewhile the links provide the horizontal components of movement of thehead relative to the elevator. Thus, the pivotal axes of the ends of thelinks opposite from the head are in fixed relation to the elevator, butare not in fixed relation to the path of movement of the head, whichpath includes both components of horizontal movement due to the linksand of vertical movement due to the elevator.

In the present structure, however, the parallelogram linkage means is soarranged that the pivotal axes of the ends of the links which areopposite from the head are in fixed position relative to the die andpress, as distinguished from a fixed position relative to an elevatorwhich moves relatively to the die and press. Consequently, these axes atthe opposite ends of the links from the head remain at all times infixed position relative to the path of the head, because both verticaland horizontal components of movement of the head are dictated entirelyby the parallelogram linkage means.

Having thus described our invention, we claim:

1. A stretch wrapping unit comprising a stretch head arranged to grip amargin of a sheet of stock and to apply tensioning force along onedimension thereof for stretching the stock and wrapping the stock whileholding the stock under tension over a male die when the head is movedalong a predetermined fixed invariable path;

quadrilateral linkage means for the head;

means connecting one end of the linkage means to the head with thepivotal axes of the linkage means at said one end parallel and in fixedposition relative to the head;

supporting means connected to the other end of the linkage means andsupporting said other end with the pivotal axes at said other end infixed position relative to each other and to said path;

all of the axes of the linkage means being parallel to each other; and

said linkage means constraining the loading face of the head to apredetermined position with respect to the adjacent end of the die atthe end of the forming operation wherein the loading face has veryclosely approached said adjacent end.

2. The structure according to claim 1 wherein each quadrilateral linkagemeans comprises a plurality of quadrilateral linkages, and thequadrilaterals defined by the four pivotal axes at the comers,respectively, of the respective quadrilateral linkages being substantialduplicates of each other.

3. The structure according to claim 2 wherein the linkages arepositioned so that corresponding corners have common pivotal axes,respectively.

4. The structure according to claim 1 wherein a male die having a convexforming face is provided and the supporting means are in fixed positionrelative thereto and maintain said other end of the quadrilaterallinkage means with the pivotal axes at said other end in fixed positionrelative to the die.

5. The structure according to claim 1 wherein the sole support of thehead is by the said supporting means and linkage means.

6. The structure according to claim 4 wherein the die has a firstportion body integral with a portion having the forming face, said firstbody portion is the supporting means, and the pivotal connections of thequadrilateral linkage means with the first body portion are spaced fromthe surface of the face and extend generally transversely relative tosaid surface and die.

7. The structure according to claim 1 wherein power means are providedfor moving the head along said path.

8. The structure according to claim 1 wherein two opposite sides of thequadrilateral linkage means are compression resisting links, each linkis pivotally connected at one of its ends to the head and at the otherof its ends to the supporting means;

and the other two sides of each quadrilateral linkage means are rigidportions of the head and of the supporting means, respectively.

9. The structure according to claim 1 wherein the head is elongated inthe direction of said linkage axes, the linkage means includes at leasttwo quadrilateral linkages which are connected to the head at theopposite ends of the head, respectively.

10. The structure according to claim 1 wherein a second stretch head isprovided and is disposed in spaced relation to the first mentioned head;

quadrilateral linkage means are connected to the second head and to thesupporting means for constraining the second head to movement along asecond predetermined fixed invariable path in a direction generallytoward and away from the first mentioned head; and the length of thelast mentioned quadrilateral linkage means is different from the lengthof the first mentioned linkage means.

References Cited UNITED STATES PATENTS 9/1956 Oeckl 72297 4/1967Mackenzie 72--450 US. Cl. X.R.

